Don't want to give paid-up letters

Appalling service from these people. I have been asking them to send me my 2 paid up letters for my 3 debts I have with them but they wont. I get calls from them everyday by different agents and all of them promise to send me those letters. They don't want to send them because they know that they want to call me again after years have passed and say that I have an unsettled debt with them and I wont have proof that its paid-up. Its been close to 3 months now asking for those letters. How difficult is it to just acknowledge that I have settled a debt and send me the letter?